For driving piles, pile planks etc., steam rammers have been in use for about a century, in which a drop hammer is connected with the piston of a steam cylinder in order to lift the hammer on admitting steam, which hammer will drop by its own weight as soon as the steam is released.
A disadvantage of such steam devices is that a bulky steam boiler is required, and that it takes a considerable time before the boiler reaches the required temperature, so that during interruptions the heating is often continued which leads to useless fuel consumption. Moreover all sealings, especially for the piston and piston rod, should be resistant to the temperature and corrosive action of steam. An additional disadvantage is the air pollution caused by such steam boilers which are, in general, of a very simple construction, and cannot be heated in the most economic way, and further it is not always possible to use fuel of high quality.
When internal combustion engines become available, which could be used for driving air compressors, it was repeatedly tried to use compressed air instead of steam in such ram devices. These air rammers, however, have not been satisfactory in practice, primarily because of the fact that such devices do not operate with the required speed. When attempting to increase the speed by increasing the air pressure, also the lifting speed increases, so that the hammer will hit its upper stop with a greater impact force which leads to energy losses and possibly to damage. The air rammers now in use are exclusively so called rapid percussion hammers in which compressed air is also used for driving the hammer towards the pile cap.
As appears from U.S. Pat. No. 2,975,761 (1961), improvements of steam rammers are still proposed, which proves that such steam devices still meet the actual needs, as the rapid percussion hammers are not suitable for many purposes.
There are also known repetitive action air hammers, in which a piston is moved in both directions by air pressure, such an arrangement being disclosed, for example, in Gunnell U.S. Pat. No. 6,322,262.
As a substitute for steam rammers so called Diesel rammers have been used for many years, in which the hammer is lifted by an explosion in a lifting cylinder, but it is not possible to make short strokes with such a device, as is necessary for initially driving the top of a pile into the soil, since a short stroke provides an insufficient compression in the cylinder. Moreover such devices produce disagreeable exhaust gases.